Surgical procedures frequently require the ligation of blood vessels, severed tissues or other organs. For this purpose, it is well known to use surgical clip appliers that advance and clamp a clip to the selected vessel, tissue or organ. See, e.g., U.S. Pat. Nos. 5,084,057, 4,616,650 and 3,086,208. Because the surgeon will typically apply many clips during the course of an operation, it has been preferred that these clip appliers contain a plurality of automatically advancing clips. Accordingly, an advancing mechanism that feeds the clips one at a time into the clamping mechanism has been necessary.
In the patents referred to above, the clips are arranged sequentially along a longitudinal axis of the clip applier. A spring is located behind the proximal-most clip and is biased to urge all the clips distally. Using the spring to advance the clips, however, is unreliable because the spring force can cause the clips to move forward with excessive force, resulting in the clips frictionally jamming against each other or getting wedged within the clip applier. Alternatively, if the frictional load on the clips is greater than the applied spring force, there will be no advancement. Also, it is possible that more than one clip at a time may advance into the clamping mechanism.
U.S. Pat. Nos. 4,452,376 and 3,899,914 disclose clip appliers wherein the clips are mechanically advanced by the operator who actuates a push bar that engages the proximal-most clip, pushing all the clips forward. While the push bar gives the operator more direct control over advancement of the clips, there still exists the problems of clip jamming and improper feeding because the clips are not visible to the operator, making it difficult to determine whether excessive force is being applied during advancement. U.S. Pat. No. 4,452,376 also describes a pawl configured to conform to the bail portion of the proximal-most clip that prevents the clips from moving proximally after advancement. The pawl, however, relies only on frictional forces to prevent rearward motion of the clips, which in some instances may be inadequate to hold the clips in place.
In another type of clip applier, the plurality of clips are advanced by a feed ratchet and a backstop ratchet. Teeth are stamped out of the ratchet bodies to contact each clip individually. Feeding occurs through reciprocating movement of the feed ratchet relative to the backstop ratchet. During clip advancement, the feed ratchet teeth push the clips forward and the backstop ratchet teeth flex out of the way as the clips pass by. When the feed ratchet is pulled back and reset, the backstop ratchet teeth prevent the clips from moving backward and the feed ratchet teeth flex out of the way as they pass over the clips. For additional details of this type of clip advance, see U.S. Pat. Nos. 4,624,254, 4,500,024, 4,452,357 and 4,430,997.
The ratchet type of clip advance reduces the problem of clip jamming because each clip is individually engaged by the teeth of the feed and backstop ratchets. The mechanism, however, does have its disadvantages. For example, the teeth themselves may become jammed during flexing, which could result in improper advancement or a failure to advance the clips. Additionally, if the teeth do not retain sufficient resiliency, they may fail to properly engage the clips during advancement or may fail to prevent their proximal movement after advancement.
In another type of clip advance, the clips are attached to a moveable belt structure having retainers that engage each individual clip, U.S. Pat. No. 5,192,288. In this device, however, the belt structure and its actuation adds an additional element of complexity to the overall design.
Accordingly, it should be appreciated that there is still a need for an improved clip applier that positively engages and advances a plurality of clips, without jamming or misfiring. Such a clip advance should also have a simple and effective construction and be easy to use.